This is meant to be a bit similar thread to what we have about ruleset changes on the ruleset forum. Tileset format just usually changes much much less than ruleset format.

There has been added optional "for_ruleset" field to .tilespec format: patch #7577

Tileset can specify what ruleset it's primarily meant for. If that information is present, client-forked server will use that ruleset from the launch - even before client first connects to change the ruleset. This should solve problem familiar from the ancients modpack that tileset incompatible with default ruleset cannot be used when launching server from the client as server is always launched with default ruleset until client connects and changes it.

You can add a unit icon that indicates that the unit wants the player to clarify what it should do. (The unit will pop up the action selection dialog when selected) Define it via the new unit.action_decision_want tag.

The key darkness_layer was removed. When darkness is drawn is now controlled by the layer_order flag through the layer named "Darkness" (see above). If you used darkness_layer=0, you can safely remove it; else take a look at the changes in alio.tilespec.